Brake control means



Octf 11, 1932s. B. s. AIKMAN 2,132,913

BRAKE CONTROL MEANS Filed July 6, 1955 INVENTOR EmRToN 5. AIKMAN ATTORNEY Patented Oct. 11, 1938 UMTED STA-TES PATENT OFFICE i BRAKE coN'rrRoLMEANS Burton S. Aikman, Wilkinsbur'g, Pa., assignor to The WestinghouseAir Brake Company, Wilmerding, Pa., a corporation of PennsylvaniaApplication July 6, 1935, Serial No. 30,121

' Q 2s claims.V (o1. sosiy My invention relates to brake control meansfor vehicles and more particularly to means for controlling brakingequipment to' prevent the Wheels from sliding.

My invention has application to iiuid pressure brake equipment employedon railway trains and traction vehicles and is effective tointermittently counteract the eect of high brake cylinder pressureduring a brake application, at sufficiently frequent intervals, toprevent a highk braking force from being maintained for a length of timeat any one time that is suiiicient to cause actual wheel sliding as thevehicle speed reduces, and to simultaneously cause a gradual reductionin high brake cylinder pressure to a predetermined low value.

It is well known that for a given braking pressure, friction type brakesare less effective in retarding the motion of a vehicleiat'high speedthan at low speed because the coeicient of friction between the rubbingVparts is lowerV at high speed than at low speed. When a full service oremergency brake application is made at high speed the brake cylinderpressure developed will exceed the pressure required to slide the wheelson the rails as the speed of the vehicle decreases. In order to bring avehicle to a stop quickly, it

has been the usual practice for an operator to` apply the brakes with ahigh degree of braking pressure at high speed, and, as the speed of thevehicle decreases,fto so operate the brakes as to cause the brakingpressure to decrease rin such manner that the vehicle is brought toalstop quickly and smoothly, without sliding of the Wheels. v

considerable danger of the wheels sliding on the L rails.

It is therefore desirable to provide, as a part of the brake equipmenton high speedtrains and vehicles, means for automatically'reducing thebraking force suiiiciently to permit the'wheels to maintain rotation andprevent their sliding Von the rails.

It is an object of my invention tovprovide a brake equipment having abraking force releas-vk ing characteristic to intermittently relieve'the' eilect of high brake cylinder pressurersuiiiciently to preventwheel sliding. e

ervoir 2 through a brake cylinder pipe 4 in ac- When such braking forceisk It is another object of my invention to provide a braking forcereleasing device which operates intermittently to progressively reducebrake cylinder pressure during a brake application.

It is a further object of my invention to provide a brake forcereleasing device for intermittent reduction'of brake cylinder pressure,the frequency of operation of which is such that a high brake cylinderpressure will not be in force a suicientvlength of time at any one time,as 10 the vehicle speed decreases, to cause actual Wheel sliding at theexisting vehicle speed.

Other advantages and objects of my invention Will appear from thefollowing description of a specific embodiment thereof taken inconnection with the accompanying drawing, in which Fig. l is adiagrammatic view of apparatus comprising a brake equipment arranged inaccordance with one preferred embodiment of the invention, 20

Fig. 2 is a view in vertical section through the brake cylinder and thebraking force releasing mechanism, and f Fig. 3 is a sectional viewtaken on line 3 3 of Fig. 2. Y

Referring to the drawing, a uid pressure brake equipment is illustratedin Fig. 1 in which a brake cylinder VI is provided and is supplied withfluid under pressure from an auxiliary rescordance with the operation ofa triple valve device 3 as controlled by the pressure in a brake pipe 5in the usual way. A brake cylinder piston rod or stem 6 is operated inaccordance with the supply of fluid under pressure to the brake cylinderI and is connected to the lever system including levers 1, 8 and 9, thelever I being connected to operate the levers I0, II, I2 and I3, whichare pivotally connected together for operating theA brake shoes I5 andI6 against the YWheels I1 and I8, respectively, that roll along the railI9. 'The upperend of the lever I3 being pivctally'connected to the carframe I4, the lever V9 of the brake equipment similarly controls theoperation ofthe pivotallyfinterconnected levers stem 6,- and the upperend of the lever 9 is conneoted to a bifurcated portion 32 of thepressure head of the brake cylinder I, so that movement of the crosshead3| away from the pressure head, 55

and of the interlinked lever system connected thereto, causes anequalized application of braking forces to the wheels l1, I9, 28 and 29.

The operating mechanism for the braking force release device 33 isconnected to the pressure head of the brake cylinder l, as best shown inFig. 2, and operates from brake cylinder pressure to partially reducethe braking force below a value corresponding to brake cylinder pressureat intervals determined by the timingr of the releasing device.

The brake cylinder l comprises a casing enclosing a piston chamber 34containing a piston 35 that is connected tc the piston stem or rod 5which lextendsr outwardly kthrough the nonpressure head 39 of thebrakecylinder I, and which is surrounded by a release spring 31, one endof which engages the piston 35 and the other end of which engages thenon-pressure head 3G to bias the piston 35 toward-the right to a brakereleasing position. The braking force release mechanism 33 comprises akcasing enclosing a valve chamber 38 containing a spring-Weighted valvepiston 39 that is urged toits seat by a spring 4| to close communicationfrom the piston chamber 34 through' passages 42 and 43, to a pistonchamber 44 containing a piston 45 that is provided with a stem or pistonrod Gil.

The braking force releasing mechanism also contains a piston chamber 46containing a piston 41, illustrated as positioned against a stop 48, andprovided with a stem49 that extends centrally through the spring 4I, theend acting as a stop for limiting the movement of thev valve piston 39away from its seat. A chamber 5l between the valve piston 39 and thepiston 41 is connected to the atmosphere through an exhaust port 52 sothat the pressure Within the chamber 5l is continuously at atmosphericpressure. A restricted passage 53 through the piston 41 permits thegradual escape of uid under pressure from the piston chamber 46 to theatmosphere.

A valve chamber 54 is provided, containing a spring-weighted valvepiston 55 that is urged to its seat 56 by a spring 51, the lower end ofwhich engages the valve 55 and the upper end of which engages the wallor partition forming the under side of the chamber 5I. The valve piston55 controls communication between the passage 43 and the piston chamber44 through passage 58 to the piston chamber 46.

The piston 45 is attached by a pin 59 to a piston rod 6l that is pivotedby the pin 62 to a lever 63,

the Vupper'portio-n of which is provided with jaws 94 and 55 forgripping the piston rod 6 and moving it slightly to the right, againstthe pressure in the piston chamber 34, upon the movement of the piston45 and the piston rod 5| toward the left, The lever 93 is pivotallyysupported upon .a pin 66 carried -by a link 61, the

, other end of which is pivotally supported by a` pin 98 onthenon-pressure head 33 of the brake "rod 9 Iv and the piston 45 towardthe rightto per- V cordance with changes in pressure in the piston mallylimited by the average adhesion of the car wheels to the rails. If thebrake shoe forces exceed this permissive value the adhesion of the carWheels to ,therails is insufficient to prevent the wheels from sliding.Tests show, however, that'a brief period of time exists between what isknown as incipiency of Wheel sliding .and actual wheel sliding, that is,a brake shoe pressure sufficient to cause wheel sliding can be exertedfor a short time without actually causing such sliding Y `due to thetime element involved.

. As the brakes are applied and brake cylinder pressure increases withinthe piston chamber 34 to a predetermined value, the spring-weightedvalve piston 39 will be forced from its seat 49 toward the right againstthe bias of the spring Y 4|, 'thus permitting fluid under pressure to owfrom the piston chamber 34 at piston chamber pressure, through passage43,. to the piston chamber 44 to force Vthe piston 45 and piston rod 6Iytoward the left, and to rock the lever 63 in a clockwise direction tocause the jaws 54 and 65Y at the upper end thereof to grip the pistonrod 5, through which the brakes are applied, and exert force thereonopposing the force exerted by the pressure within the piston chamber 34,thus slightly decreasing the degree of application of the brakes belowthat corresponding to brake cylinder pressure. The degree of applicationof the brakes will be reduced both by reason of the force exertedthrough the lever 63, and because of the reduction in the pressure ofthe fluid in the brake cylinder chamber 34 as. the result of the supplyof fluid under pressure therefrom to the release mechanism 33. As thepressure builds up in the piston chamber 44 and in the passage 43 tobrake cylinder pressure, the weighted valve piston 55 is, at apredetermined pressure, also forced upwardly from its seat 55 againstthe bias of the spring 51, thus permitting the flow of uid underpressure at brake cylinder pressure from the passage 43 through passage58 to the piston chamber 46 to move the piston 41 against the bias ofthe spring 4I until the piston stem 49 engages the valve piston 39 andforces it to its seat 40.

It will be noted that the area of the valve chamber 38, subject topiston chamber pressure after the valve piston 39 has been moved fromits seat, is of considerably greater area than the central portion ofthe valve piston 39 that is subject to brake cylinder pressure when thevalve piston 39 is seated. As the result ofthe differ- Y ential force onthe'valve piston 39 tending to urge it against the bias of the spring 4iwhen the 4 valve piston is seated and when it is unseated, aconsiderable drop in brake cylinder pressure below the valve necessaryto unseat the valve piston 39 is required before the valve piston willagain seat, due to the pressure ofthe spring 4I thereon. It will also benoted that Ythe area of the piston 41, that is subject to'brake cylinderpressure after the valve piston 55 has become unseated, is greater thanthe area of the valve piston 39 that is subject to brake cylinderpressure in the valve chamber 38, so that, as soon as pressure-builds upto a predetermined value in the piston chamber 45, the piston 41 actingthrough the stem 49 will force the valve piston 39 to its seat 49, andthereby cut off the supply Yof fluid under pressure from the brakecylinder chamber 34 to the chamber 38 of the release mechanism 33, andprevent a further reduction in the pressure of the fluid in the brakecylinder CTI chamber 34.l Fluid under pressure is released valve pistonr39.1 l

gradually from the piston'cnamer 46,` and from the piston chamber4'4ran`d the valve-chamber 38;

'through the restricted passage 53"andport.52

til fluid pressure acting on the f'valve piston has been reduced to 'avconsiderable degree 2less .than

the degree of uid pressure required to open the valve. V-The effect ofthe differential-:areas betweenV the central portionffof the valvepiston 55,y that is subject to the pressure withinrthe passage 43, andthe larger area o-f -th'e valvepiston, that is subject tothe pressure:within the valve chamber 54, is to require a considerable vdecrease inpressure within the passage :43 and fv'alve chamberV 54, after the valvepiston has been unseated, below the value necessary to unseat it,4before :the valve piston will again seat. SW-hen, as `a result of therelease of fluid under pressure tothe'atmosphere through the restricted.passagei53 `in the piston 4l, the pressure -in the valvechamber 54 hasbeen reduced vsufeient'lyto permit the valve piston 55 to seat, thepressure in the piston chamber 44 will have permitted the piston '45 tobe moved to its illustra-ted position by the spring 69, thus disengaginglthe jaws; 64 and 65 from the piston rodY v6 and permitting. the brakesto be. applied to a value corresponding to the pressure Within thepiston. chamber '34 fof the brake cylinder AI. 'Y As the pressure withinthe piston-chamber` 46 decreases due to the release of fluidunderpressure through the restricted passage 53, theiorce of the pistonstem 49 against 'the valve :piston 39 is reduced, and the piston 41and.stemr49 :are

moved by the force of the spring 4l against v,the

l stop 48, as illustrated, thusjpermitting'the valve piston 39 to againbe unseated due to themes'.-v sure withinthe piston chamber v34 asapplied. to the central smaller area Aof the valve piston 39 throughpassage 42, thus repeating the-cycle ofV operation just above described,causing the piston 45 to be forced to the vleft to again/exert -force`on the piston rod l6 `tending Ato -move Yit 4'toward the right todecrease t-he brake shoe `pressure somewhat below that corresponding tobrakecyl-A inder pressure within Athe piston Ichamber 34, while'thepressure ofthe iluid in the brake cyliri` der chamber 34 is furtherreduced -by'the supply of fluid therefrom to the releasing mechanism33.

Likewise, as the pressure withinr'the piston cham:

ber 44 builds iup to a valuesuicienttoexertf Vsubstantial force on thepiston: 45, the pressure of fluid supplied from thebrakecylinderthroughthe passage 43 will build up to a `value sufiicient seat against thebias of the spring'l -andreiect the supply of `fluid under pressure `tothepiston chamber 46 to again 'cause the seating-of `the These cycles-of operation are repeated until thepressurein the piston chamber 34 ofthe brake cylinder I has Vdecreased to yavalue depending upon thesetting of the'spring 4l belowwhich the fluid vat brake cylinderlpressure, vsupplied through the passage'42 to the Vseated area;of Y

valvepiston A3ilyisinsuilicient to force the valve piston 39 from itsseat 40. Y Y

-It will be noted 'that immediately afterthe brake cylinderpressure hasbeen `increased tofa y by the supply of fluid under pressure from thebrake cylinder to the release mechanism 33, with the result that theydegreeof brake application which 'the brake cylinder can effect iscorrespondingly reduced.1 At a short time interval thereafter the lever63 is` permitted to move in 4a co'unterclockwise direction to releaseits grip upon Ythe piston rod 6 and permit the reapplimation of thebrakes tothe full value of brake cylinder pressure,which-, aspointed outabove, has been vreduced somewhat bythe release of vfluid therefrom. Thefrequency 'of operation o the partial release of thebrakes is' such thathigh brake lcylinder pressure willnot continue `for a sufficient lengthofjtimeftofeffect actual Wheel sliding 4but will beV reduced at 'theincipient stage of wheel sliding.

means of relieving the brake shoe -pressure will reduce in smallincrements the brakecylinder pressure and the 4brake shoe 'pressureresulting therefrom, so that, -as the speed of the train is reduced,'and the coeflicient lof friction between the brake shoes "and 'the car'wheels is increased, the brake cylinder pressure will be reduced at arate to provide 'the 1maximum rate of deceleration of the vehicle untila Alow vehicle speed is reached, when the brake cylinder pressure willhave been reduced to such value that the braking Vforces will produce asmoothl stop.

While one preferred embodiment of-my-invention has been illustrated landdescribed, it will be Vapparent to those skilled in the lart that manymodifications `in the apparatus illustrated may be made within 'thespirit of my invention and Ido not wish tobe limitedotherwise't'haniby'the scope of the'appended claims.

Having 'now described my invention, what nI I claim'as new and desire tosecure by-Letters Patent, is:

1. Ina brake equipment for vehicles, 'a vbrake cylinder, means forsupplying fluid under :pressure to said 'brake cylinder to apply thebrakes, and means subjectlto brake cylinder pressure and operative upona predetermined brake `cylinder pressure for effecting va partialrelease :df `the Vbraking force 'occasioned Vby the-brake cylinderpressure for a short interval vof time, and for thereafter interruptingsaid brake releasing force toipermitfreapplication'of the brakes'to avalue corresponding -to brake'cylinderlpressure.

2. Ina brakelequipment for vehicles, abrake cylindenmeansl for supplyingiiuid under pressure to saidgbrake cylinder to'apply=the brakes, toforce the valve piston upwardly' from its l and means subject -to brakecylinder pressure and operative upon a predetermined brake -cylinderpressure for effecting a partial 'release of 'the braking forceoccasioned by .thebrake vcylinder 3 pressure for effecting a-reductioninthelbraking force below that correspondingztolbrake cylinderpressure, meansfsubject to the operation of said last mentioned meansfor aeffecting a predeter-A mined reduction in brake cylinder pressureand for effecting a reapplicationjof the brakes in accordance with brakecylinder pressure.

4. In brake equipment for vehicles, .a brake `cylinder, meansforsupplying fluidr under pressure to said .brake cylinder to apply thebrakes, means for preventing the sliding of the Wheels comprising meansresponsive to a predetermined brake cylinder pressure for effecting areduction in the braking force below the value corresponding to brakecylinder pressure, a reduction in lbrake cylinder pressure, and a fullapplication of the brakes in accordance with the reduced brake cylinderpressure.v

. 5. In abrake equipment .for vehicles', a brakel cylinder, meansgforsupplying iiuid under pressurewto said brake cylinder to apply thebrakes,

means subject to Vbrake, cylinder pressure andV operative upon apredetermined brake cylinder pressure for effecting a recurring decreasein braking force belowthat corresponding to brake cylinder Vpressure-aireduction in brake cylinder pressure, and a reapplication of the brakesin ac-Y cordance with brake. cylinder pressure.

6. In a brake equipment for vehicles, a brake cylinder, means'forsupplying fluid under pressure to said brake cylinder tofapply thebrakes, means for preventing wheel slipping comprising means forintermittently effecting a reduction in brake cylinderv pressure and foreffecting an alternate reduction in the braking force belowbrakecylinder pressure and a reapplication of thebrakes in accordance withthe reduced brake Y cylinder pressure. v

'7. In a brake equipment for vehicles, a brake cylinder, means forsupplying fluid under pressure to said brake cylinder to apply thebrakes, a braking force reducing means subject to brake cylinderpressure and operative upon a brake cylinder vpressure above apredetermined value for effecting a 4reduction in braking force belowthat corresponding to brake cylinder'pressure, means responsive to theoperation of said last named means for effecting a reduction in brake vcylinder pressure and for` interrupting the operation of said brakingforce reducing means to permit a reapplication of the braking force to avalve corresponding to the reduced brake cylinder pressure. v

8. In a brake equipment for vehicles, a brake cylinder, means forsupplying fluid under pressure to said brake cylinder to apply the'brakes, a braking force reducing means subject to brake cylinderpressure and operative upon a Ybrake cyl-V sure to said'brake cylinderto apply the brakes,`

means for reducing the sliding of the Wheels on therails comprising apressure operated braking force reducing means for reducing the degree'of' V,application of the brakesbelow a value correspending tothepressure on the brake cylinder piston, a weighted valve subject tolic-rake cylinder pressureforeiectingthe supply of uid under pressure tosaid pressure operated means, and means subject to the pressure inY saidpressure operated means for interrupting the operation of said brakingforce reducing means.

10. In abrake equipment for vehicles, a brake der pressure foreifectingthe supply of fluid under pressure from said brake (cylinder to saidpressure operated means, and means subject to the pressure irl-saidpressure operated means fory interrupting the 'flowA of fluid runderpressure from said brake cylinder and for gradually releasingfluidrunder pressure from said pressurel operated braking forcereducingmeans to effect a reapplication of the brakes in accordance with brakecylinder.- pressure. Y. ,l Y

V11. In a brake equipment-for vehicles, a brake cylinder, means forsupplying fluid under pressure to said brake cylinder to apply thebrakes, means forreducing the sliding of the wheels on the railscomprising a pressureoperated braking force reducing means for reducingthe degrec of application of the brakes'below a valve corresponding tothe pressure on the brake cylinder piston, a weighted valve'subject tobrake cylinder pressure for effecting the supply of fluid' underpressure from said brake cylinder to said pressure operated means uponanincrease in brake cylinder pressure above a predetermined value, andmeans subject tothe pressure in said pressure operated means .forinterrupting the operation of said braking force reducingV means and foreffecting a reduction in brake cylinder pressure upon the increase inpressure in said pressure operated means above a predetermined value.Vy. x

12. Ina brake equipment for vehicles, a brake cylinder, means forsupplying fluid under pressure to said brake cylinder to apply thebrakes, means for reducing the sliding of the wheels on the railscomprising a pressure operated braking force reducing'means forYreducing the degree of application of the brakes below a valuecorresponding to the pressure on the brake cyiinder piston, a Weightedvalvey subject to brake cylinder pressure for effecting the supply offluid under pressure from said ubrake cylinder to said pressure operatedmeans, a weighted valve subject to the pressure in said pressureoperated means forv effecting the movement of said rst named A cylinder,means for supplying uid under pressure to said brake cylinder toapplythe brakes, a braking force reducing meanssubject to brake cylinderpressure and operative upon a brake cylinder pressure aboverapredetermined value for effecting a reduction in braking force belowthat correspondingr to brake cylinder pressure comprising a pressureoperated means for opposing tlie effect of saidV brake cylinderpressure,- valve means for effecting the supply Vof fluid under pressurethereto in 4accordance with brake cylinder pressure, and means for,Veffecting a partial, release of fluid under pressure therefrom" Y toVinterrupt the operation of said braking forcereducing means. Y

14. In a brake equipment for vehicles, a brake cylinder, means forsupplying fluid under pressure to said brake cylinder to apply thebrakes, a braking force reducing means subject to brake cylinderpressure and Aoperative upon a Vbrake cylinder pressure above apredetermined-value for effecting a reduction in braking force belowthat corresponding to brake cylinder pressure andl comprising pressureoperated` means for opposing the effect of 'said brake cylinderpressure,1valve means for effecting the supply Yof fluid under'pressurethereto in accordance withV the brake cylinder pressure, and means for'effecting a partial release of uidunder pressure from said brakecylinder and from said pressure operated means toA eect a reapplicationof the brakes in Yaccordance lwith "the reduced. brake cylinderpressure. A.

15. In a brake equipment for vehicles, a, brake cylinder, means forsupplying'fluid under pressure to said brake cylinder to applytheibrakes, a braking force reducing means for reducing the brakingforce below the value corresponding to brake cylinder pressure andhavingxa braking forcereducingpressure chamber, means respon-' sive tobrake cylinder pressure abovea predetermined value for effecting thesupply of'fluid under pressure to said chamber at brake cylinderpressure,.pressure operated means for interrupting the supply of fluidunder pressure to said braking force reducing pressure chamber, meansresponsive to the pressure in said pressure cham- Y berabove apredetermined Value for supplyingA fluid under pressure toVV saidpressureoperated means, and means forV releasing fluid under pres-- surefrom said braking force reducing pressure chamber and from said pressureoperated means to effect the release of said braking force reducingmeans to permit the reapplicationj of a braking force Vin accordanceWithbrakecylinder pressure, and therelease of said'pressure operated'means to permitfurtheroperation of the means responsive to brakecylinder vpressure foreffecting a subsequent operation of saidbrakingforce reducing means. i

16. In` a brake equipment for`vehicles, abrake cylinder, means forsupplying 'fluid under pressure to said brake cylinder to apply thebrakes,`

a braking force reducing means for.V reducing the braking force belowthe value corresponding to brake cylinderipressure having a brakereducing pressure and chamber, means responsive tobrake cylinderpressure above apredeterrnined value for effecting the supply offluid'under pressure from said brake cylindert'o said chamber, pressureoperated means Vfor interrupting the supply or" fluid underpressure tosaidbrake reducing chamber, means responsive to the pressure in saidpressure chamber above a 'predetermined value for supplying fluid underpressureV cylinder pressure, and a release of said pressure i operatedmeans to permit further operation of' said means responsive to brakecylinder pressure for effecting a subsequent operation of said brakingforce reducing means.

17, In a brake equipment for vehicles, a 'brake cylinder, means forsupplying fluid under pressure toY said brake cylinder toapply thebrakes, a braking force reducing means forv reducing .the braking forcebelow the value corresponding to brake vcylinder pressure, having abrake rreducing pressure chamber and a weighted valve Vresponsive tobrake cylindery pressure above a predetermined value for effecting thesupply of l fluid under, pressurefrom said brake cylinder to saidchamber, apressure operated means having a stem for urging said weightedvalve to its seat, and means responsive to the pressure in said pressurechamber above a predetermined value for Vsupplying :fluid under pressurefrom said pressurefvchamber to said pressure operated means4toeffecuarelease of said braking force 18.,In a fluid pressure brake,in combination, a brake cylinder,- a,brake cylinder piston therein,means for supplying fluid under pressure to said brake cylinder, avpiston, means for operatively connecting said piston to the brakecylinder piston to oppose the pressure on the rbrake cylinder pistonbythe fluid pressure acting on saidopposing piston,'and means operatedupon Va predetermined increase in brake cylinder presder piston tooppose the pressure on the brake cylinder piston;A by the fluid pressureacting on said opposing piston,va1ve` meansy operated upon avpredetermined increase in brake cylinder pressure for'y supplying fluidunder kpressure to said' opposingV piston, and means operated upon apredeterminedzincrease vin `the pressure of fluid supplied tosaid.opposing piston for operating said pvalve meansto cut off the supply offluid to 'said opposing piston.

20. InA auid pressure brake, inr combination, a brake cylinder, meansfor supplying fluid under.. pressure toe the brake cylinder, Y.mechanismoperated upon a predetermined increase in brake cylinder pressure forreducing'the braking force eilected by .the'increase'in brake cylinderpressure,r and means operative after a predetermined time intervalV forcutting said mechanism out of action.

' 21. Ina fluid pressure brake, in combination, a brake cylinder, meansfor supplying fluid under pressure to the Vbrake cylinder, mechanismoperated upon' a predetermined increase in brake cylinder pressure forinterposing a force to oppose the.` braking force set up by the increasein brakeV cylinderY pressure, Hand means operated after a predeterminedtimelintervalfor relieving said opposing force.

22. In aiuid pressurebrake, in combination,

va.'lirake cylindena piston in said'brake cylinder and operable on anincrease in the'pressure of the fluid therein to exertiforc'e to effectan application of the brakes, an ropposing piston `operative on anincrease in the pressure of the fluid supplied thereto to exert forceopposing the force exerted by saidbrakecylinder piston,`and'meanssubject to and operated on a. predetermined increase in the pressureofthe fluid supplied to the'brake cylinderto`supp1y fluid from the brakecylinder to said opposing piston to'l reduce the braking force below thevalue corresponding to the brake cylinder pressure and to also reducevbrake cylinder pressure.

23. In a fluid pressure brake, in combination, a

brake cylinder, a piston in said brake cylinder and operable on anincrease in the pressure f the fluid therein to exert force to effect anapplication of the brakes, `an opposing piston operative y on'anlincrease in the pressure of the fluid suppliedthereto to exert forceopposingthe` force Aexerted by said brake cylinder piston, means subjectto and operated on a predetermined increase in the pressure of the fluidsupplied to the brake cylinder to supply uid from the brake cylinder tosaid opposing pistonv to reduce the braking force below the valuecorresponding'to the brake cylinder pressure and to also reduce brakecylinder pressure, and means subject to and operated on a predeterminedincrease in the pressure of the fluid supplied to the opposing pistonfor cutting off the supply of fluid to said piston and for releasingfluid therefrom.

24. Ina vehicle fluid pressure brake equipment,v in combination,brakingimeans, application means operative on an increase in thepressure of the-fluid in a pressure chamber to exert Y valve means forsupplying fluid under pressure from said pressure chamber to saidcontrolchamber, whereby the degree of application of said f braking' means isreduced by the reduction in the pressure `of the fluid in saidY pressurechamber Y and by operation of'said releasing means, said valvemeans-being thereafter operative to cut off the supply of fluid underpressure from said pressure chamber to said control chamber and torelease lluid from said control chamber to elect arreapplication of thebraking means by said application means to a degree Vdetermined by thepressure of the fluid remaining in the pressure chamber( 25. In a fluidpressure brakeequipment for a vehicle having a Wheel, in combination, abrake cylinder, apiston mounted insaid brake cylinder and having anapplicationv chamber Hfat the Y face thereof,said piston being operableon an increase in the pressure of the fluid in said appli-V cationchamber toexert braking. force varying in accordance with the increaseinthe pressure of the fluid in said application chamber, meansA forsupplying fluid under pressure to saidv application chamber and tothereafter Vcut off the sup# ply of' fluidunder pressure to saidapplication chamber, releasing means operative on' an 'increasein lthepressure/of the fluid in a pressure chamber to exertforce opposing thatof the brake cylinder piston, means for releasing fluid under pressureVfrom said application chamber and to thereafter cut o'ffitherelease offluid from said chamber to` maintainY the pressure Vtherein at a lowervalue than that initially present therein to therebyreduce the brakingforce created by said brake 'cylinder piston, means for supplying fluidunder pressure to said pressure chamber concurrently with the release ofuid from said application chamber to thereby cause'the effective brakingforce created by saidbrake cylinder piston to be reduced belowthe valuecorresponding to application chamber pressure, and means brakes.

areas 13 Y of the brakes in accordance with the reduced applicationchamber pressure.

26. In a fluid pressure brake equipment for a vehicle having ra Wheel,in combination', a brake cylinder, a piston mounted in said brakeYcylinder and'having an application chamber vat the face thereof, saidpiston beingoperable on an increase in the pressure of the uid in saidapplication chamber to exert braking force von said Wheel toresistrotation thereof, the degree of braking force varying inaccordance with the increase in thepressure ofthe fluidinsaid-application chamber, means for supplying fluidA under pressure tosaid application chamber to increase the pressure therein Vto avaluevwhich Vmay be sufficient to produce braking force onV said Wheelto a degree to prevent rotation thereof and to thereafter cut off thesupply of fluid under pressure to said application chamber', releasingmeans operative on an increase in the pressure of the uid in'a pressurechamber t0 exert force 0pposing that of the brake cylinder piston, meansfor supplying uid under pressurefrom said application chamber to saidpressure chamber to 27. Vehicle brake apparatus comprising a brake acylinder, brake control means operative to control kthe supplyof fluidunder pressure to and the release of fluid under pressure from the brakecylinder to effect Vapplication and release respectively of the brakes,means' providing a chamber, means effective while said brake controlmeans'is conditionedto cause application ofVV the brakes forA causingfluid under pressure to be supplied'from the brake cylinder to saidchamber to reduce brake cylinder pressurefand consequntly the degree ofapplication of the brakes,

Vand means responsive to the pressure yin said chamber for exerting aforce Yin opposition to brake cylinder pressure to further reduce theeffective degree of application of the brakes.

28. Vehicle brake apparatus comprising a brake l cylinder, brakeVcontrol means operative to control the supply ofiluid underY pressure toand the release of fluid under pressure from the brake cylinder toeffect application andVV release respectively of the brakes, meansproviding a chamber, means automaticallyA effective while the brakecontrolmeans .is conditionedtov cause application of the brakes forcausing fluid under pressure to.V be supplied from vthe brake cylinderto said chamber to reduce the brake cylinder pressure and consequentlythe degree of application of the brakes, and means responsive to thepressure in? said chamber for exerting Va force in opposition tobrakekcylinder pressure to further reduce the effective degree ofapplication of the BURTON s. AIKMAN.'

